Switchboard cord circuit



March 9, 1937. W. E. DARROW SWITCHBOARD CORD CIRCUIT Filed July 5, 1935 Q @im /A/l/EA/m/P W. E. DA RROW By A TToR/VEV Patented Mar. 9, 1937 UNITED STATS PATENT OFFICE SWITCHBOARD CORD CIRCUIT Appncatisn July 5, 1935, serial No. 29,983

6 Claims.

This invention relates to telephone systems and more particularly to universal cord circuits for indiscriminately connecting telephone lines of like or unlike character, as for example, two common battery lines, two magneto lines, or a common battery and a magneto line.

An object of the invention is to control cord circuit supervisory signals in accordance with supervisory signal current incoming over any line, of either type, with which the cord circuit is connected.

A feature of the invention in accordance with the foregoing object resides in the employment of a supervisory relay having three windings. When the cord is idle, or connected to a magneto line, all three windings are connected in series across the cord circuit talking conductor and when the cord is connected to a common battery line one of these windings is disconnected and the cord 0 circuit battery is connected in series with the remaining two windings bridged across the cord.

Figure 2 of Patent 1,931,603, issued October 24, 1933 to W. E. Darrow, the present applicant, dis-4 closes a somewhat similar universal cord circuit in which supervisory relays 2|2 and 213, each having two windings, are normally bridged across the cord circuit. This condition is unchanged when the cord is connected to a magneto line but when a common battery line is connected to a cord circuit battery is serially included in the bridge.

Systems employing the two-winding scheme, of Patent 1,931,603, are subject to limitations, particularly as regards length of magneto lines, which it is not practicable to overcome with a twowinding relay. For the condition of a cord connected to a common battery line the relay must be given a release adjustment that will insure proper functioning of the relay during subscriber flashing, release against leakage current, and other circuit conditions. VThe spring tensions that are set up by this release requirement play an important part in determining the current on which the relay will operate satisfactorily. The current in the long common battery lines is much greater than this release requirement, so that there will be nb'diiiculty in adjusting the relay for operation over common battery lines. The signaling current over long magneto lines, however, is less than that for common battery lines and the relay must therefore be given a weaker adjustment. The weakening of the operate adjustment can be carried only to a certain point because if the operate current is made too low, the relay may fail to release when it should on common battery connections. An operate current must therefore be selected sufficiently higher than the release current to permit maintaining the relay so that it will function over both common battery and magneto connections. The operate current thus determined limits the length of magneto loops.

As'contemplated by the present invention, the provision of a third winding on the relay which is connected in series with the two original windings on magneto connections increases the turns so that the relay is more sensitive to weak magneto signals. This will increase the length of magneto lines over which the relay will operate. When the cord circuit is connected to a common battery line, the third winding is disconnected and the cord circuit battery substituted therefore, hence, the relay can be given a release and operate adjustment on the two common battery windings and it will still operate satisfactorily over long magneto lines.

The invention will be understood from the following description together with the accompanying drawing which illustrates one embodiment of the invention.

In the drawing, A and B are common battery subscribers stations, C and D are magneto subscribers static-ns and E is a universal cord circuit at a switchboard in which are located line jacks |00 and |0| for the common battery stations A and B, respectively, and line jacks |02 and |03'for the magneto stations C and D, respectively.

Cord circuit E consists of answering and calling cords terminating in plugs |06 and |01, respectively, in which condensers |08 and |09 are inserted in the tip and ring conductors thereby insulating the two ends of the cord from each other with respect to direct current.

Answering and calling sleeve relays H0 and are associated with their respective ends of the cord and operate responsive Vto the connection of the associated plug sleeve with the grounded sleeve of either one of the common battery line jack E00 or |0l. The sleeves of the magneto line jacks l02vand |03 are not grounded when a plug is inserted and consequently the cord sleeve relays remain unoperated. I

H2 and H3 are answering and calling supervisory relays each provided with three windings normally connected in series across the tip and ring conductors of the respective ends of the cord over normal contacts |04 and |05 of the respective sleeve relays H0 and ||5v and ||8 are answering and calling supervisory lamps, respectively, adapted to be controlled by the respective supervisory relays I I2 and II3 when their respective ends of the cord are connected to common battery lines.

II'I is a magneto supervisory lamp, common to both ends of the cord, adapted to be lighted when a magneto station connected to either end of the cord rings on the line and operates the associated supervisory relay, the corresponding sleeve relay being in its normal or unoperated position at the time due to the absence of ground on the sleeve or the m-agneto line jack.

The operation is as follows: In response to a call from common battery station A, the operator inserts plug |06 in jack |00 thereby closing local contacts I I4 of the jack and grounding the sleeve which thereby causes the cord sleeve relay H0 to operate. Operation of relay I I0 opens its contacts |04 and ||5 and closes contacts |20 and I2I.

Opening of contact |04 disconnects the top winding of relay II2 and the closure of contacts |20 and I2I connects battery and ground respectively to the ring and tip conductors of the cord through the respective lower and middle windings of relay |I2 thereby establishing a wet or battery bridge, including two windings of relay |I2, across the cord. If the receiver at station A is off the hook at this time the loop will be closed and relay I I2 operates in the usual manner thereby removing battery at its lower contacts from the lamp I|6 and preventing it from lighting.

Upon ascertaining the number of the desired station which we will first assume to be common battery station B, the operator inserts calling plug |01 in jack I0! whereupon sleeve relay III operates to ground on the sleeve. As it is assumed that the called station receiver is on the hook, supervisory relay II3 will not operate at this time and consequently supervisory lamp ||8 will light in a circuit traced from ground, sleeve contacts of jack |0| and plug |01, lamp I|8 and lower contacts of relay II3 to battery. It is, of course, obvious that the arrangement of relays are the same at both ends of the cord and that the operation of relay III disconnected the top winding of relay II3 and connected battery and ground through the lower and middle windings of relay II3 to the ring and tip of the calling end of the cord.

When the called subscriber answers relay II3 operates in the usual manner thereby opening its lower contacts and extinguishing lamp I I 8. When either or both of the common battery subscribers hang up, their respective supervisory relays release thereby connecting battery to the corresponding supervisory lamps which light as an indication to the operator that she may disconnect.

It will now be assumed that magneto station C originates a call in the usual manner by the operation of a hand generator |23 in response to which the operator inserts plug |06 in jack |02. As this jack is not arranged to connect ground to the sleeve the cord sleeve relay I I0 does not operate and consequently all three windings of relay I I2 remain connected in series in the dry bridge across the tip and ring of the cord.

If common battery station Bis called the operation of relays III- and II3 is the same as previously described.

In case magneto station D is called insertion of plug |01 in jack |03 will not operate relay III as no ground is present on the sleeve and consequently all three windings of relay II3 remain connected in series across the tip and ring of the calling end of the cord.

When the conversation is completed it is general practice for the calling station to ring off by giving the magneto generator a short turn which transmits a pulse of ringing current over the line which passess through the serially connected windings of relay I|2 causing that relay to operate momentarily thereby closing its contact |22. Due to the fact that relay I I0 is not operated, contacts ||5 are closed and a circuit is thereby established to light the magneto supervisory lamp II'I in an obvious circuit. Lamp I|`| remains lighted only during the duration of the ring and is extinguished immediately upon its cessation.

A re-ring or ring-off signal initiated by the called station causes operation of relay II3 in a similar m-anner to that described for relay II2 and the consequent lighting of the common lamp |I-1.

Lighting of lamp I II, for any duration, is an indication to the operator that she must challenge on the line to determine whether the conversation is nished or another connection is desired by one of the stations.

What is claimed is:

1. In a universal cord circuit for indiscriminately connecting magneto and common battery lines, supervisory relays, one for each end of said cord and connected in bridge thereto, a battery, and means responsive to conection of either end of the cord to a common battery line for connecting said battery in series with said respective relay and for reducing the effective winding turns thereof..

2. In a universal cord circuit for indiscriminately connecting magneto and common battery lines, supervisory relays, one for each end of the cord, each of said relays having three windings serially connected in bridge of the respective ends of the cord when the respective ends are disengaged or connected to a magneto line, a battery, and means responsive t0 connection of either end of the cord to a common battery line for disconnecting one winding of. the respective relay from the bridge and substituting said battery therefor.

3. In a universal cord circuit for indiscriminately connecting magneto and common battery lines, plural winding supervisory relays one for each end of the cord, each of said relays having its plurality of windings serially connected in bridge of the respective end of the cord when the respective end is connected to a magneto line, a battery, sleeve relays, one for each end of. the cord, and means controlled by the respective sleeve relay when one end of the cord is connected to a common battery line for disconnecting one of the windings of the corresponding supervisory relays and for Substituting said battery therefor in series with the remaining windings.

4. In a universal cord circuit for indiscriminately connecting magneto and common battery lines, supervisory relays, one for each end of. the cord, said relays having a relatively high impedance and being connected in bridge of the respective ends of the cords when the corresponding ends are connected to magneto lines, a battery, and switching means responsive to conection of either end 4of the cord with a common battery line for reducing the impedance of the respective relays and for connecting said battery in series therewith.

5. In a universal cord circuit for indiscriminately connecting magneto and common battery lines, a supervisory relay having a relatively large number of turns connected in bridge to one end of the cord, a source of direct current, and means including a sleeve relay responsive to the connection of said end of the cord to a common battery line for reducing the elective turns of said supervisory relay and for serially connecting said source of current at the mid-point of the remaining eiective turns.

6. In a universal cord circuit for indiscriminately connecting magneto and common battery lines, a sleeve relay associated with one end of the cord and arranged to operate when the cord is connected to a common battery line and to remain non-operated when the cord is connected to a magneto line, a. supervisory relay having a relatively large number of turns connected in a bridge circuit across the same end of the cord, said circuit including a normal contact of said sleeve relay, and a battery, said sleeve relay being so arranged that when operated a substantial number of turns will be eiectively removed from said supervisory relay and said battery will be serially connected in said bridge in substitution for the turns removed.

WIRT EDWARD DARROW. 

